Many coating properties often generically referred to as tinctorial properties (including, for example, colour intensity, opacity and gloss) depend upon the extent of aggregation or flocculation of pigment particles (or other particulate materials) within the coating. Colour is normally introduced into a coating formulation by addition of a pigment dispersion in solvent containing a high concentration of pigment.
The pigment dispersion is generally produced by one of a variety of milling techniques to break up the aggregates of pigment particles and reduce the average particle size. Milling is often carried out in the presence of some polymeric material which is present to stabilise the dispersion and minimize flocculation of the dispersed particles. However, some pigment dispersions disperse poorly in solvent based systems.
European Patent 0 458 479 discloses a coating composition containing a dispersant and a graft copolymer of an acrylic polymer component having a tertiary amino group and/or a nitrogen-containing heterocyclic ring and a particular polyester component.
U.S. Pat. No. 5,319,045 (and JP 4-161415 A) discloses ester-type copolymers useful for resin modifiers.
U.S. Pat. No. 6,362,274 discloses graft copolymers containing at least three sequences of distinct chemical nature. The three sequences include an anchoring group, a hydrophilic group, and a hydrophobic group. The graft copolymers are useful for preparing pigment dispersions in aqueous and/or organic media.
International Patent Application WO 01/44330 discloses a composition suitable for a pigment dispersant, which contains a graft copolymer having a macromonomer grafted onto the polymeric backbone. The graft copolymer contains an amide functional group as a pigment anchoring group. The backbone may also have attached to the backbone an additional pigment anchoring group selected from an aromatic ester, an aromatic amine, an aliphatic amine, a quaternary ammonium group, or mixtures thereof.
European Patent application EP 1 182 218 A1 and U.S. Patent Application 2003/00225207, both disclose graft copolymers for pigment dispersants.
Examples of pigment types that are known to disperse poorly in solvent based systems include perylene-based pigments, anthraquinone-based pigments or quinacridone-based pigments. Attempts to disperse these pigments in solvent based systems include utilising caprolactone:polyethylene imine copolymer dispersants (EP 632 108 A), Novolak resin dispersants (JP 09291249 A), alkylene oxide based graft copolymer dispersants (disclosed in both JP 10046050 A and JP 10060360 A), and specific acrylic graft copolymers that interact with carbon black (JP 2004091610 A).
However, it is believed that none of the dispersants provide good tinctorial properties (including at least one of acceptable dispersancy, acceptable transparency, acceptable viscosity, and acceptable shock seeding) in a final coating. Thus, there is a need to disperse a pigment in solvent based systems that is capable of providing acceptable properties to a coating. The present invention provides a composition capable of dispersing a pigment in a solvent based system.